1. Field of the Invention
This invention relates to a vibration-type contact detection sensor and more particularly to a vibration-type contact detection sensor used to measure the configuration of a workpiece, etc., with a three-dimensional measuring machine, etc., for example.
2. Description of the Related Art
Hitherto, a height gauge (one-dimensional measuring machine), a three-dimensional measuring machine, a surface property measuring machine, a small-hole measuring machine, etc., has been known as a measuring machine for measuring the configuration and the dimension of a workpiece. Various probes are used for the measuring machines in order to detect the positional relation between the main unit of measuring machine and the workpiece. The probes are classified into non-contact probes and contact probes, and continuously measuring probes (or scanning probes) and trigger transmission probes (or touch probes), etc.
A vibration-type contact detection sensor 100 as shown in FIG. 10 is known as a contact-type trigger transmission probe of a measuring machine as described above (refer to Japanese Patent Unexamined Publication No. 2000-55643). The vibration-type contact detection sensor 100 comprises a stylus holder 101, a stylus 102, and two piezoelectric elements 103.
The stylus holder 101 comprises a fix part 111 and a stylus support portion 112. The fix part 111 is attached to a move shaft of a measuring machine (not shown). The stylus support portion 112 bonds and fixes the stylus 102 therein. The stylus support portion 112 is bifurcated and the stylus 102 is supported along an axial direction at two points of the bifurcate tips. Each tip of the stylus support portion 112 is angular U-shaped in cross section and the stylus 102 is positioned in the opening of the tips of the stylus support portion 112.
The stylus 102 is formed of a substantially column-shaped and is provided at a tip with a contact portion 121 for coming in contact with a workpiece.
The piezoelectric elements 103 vibrates the stylus 102 so that the stylus 102 is vibrated in the axial direction, and detects a change in the vibration state of the stylus 102 occurring when the contact portion 121 comes in contact with a workpiece. One piezoelectric element 103 is attached to the upper face and the other is attached to the lower face of the stylus support portion 112 across the bifurcate parts thereof. If the vibration conditions of the piezoelectric element 103 are adjusted so that the vibration of the stylus achieves resonance, the contact of the stylus with the workpiece can be detected with a high sensitivity.
Common electrodes are respectively formed on the lower face of the piezoelectric element 103 placed on the upper side and the upper face of the piezoelectric element 103 placed on the lower side in FIG. 10. The upper face of the piezoelectric element 103 placed on the upper side in the figure is divided into two parts, a vibrator (more particularly, electrode parts of the vibrator) 131 and a detector 132 (more particularly, electrode parts of the detector) at the position corresponding to the center between the two support points of the stylus support portion 112. In other words, the vibrator 131 and the detector 132 are implemented as a single solid-state component. The lower face of the piezoelectric element 103 placed on the lower side in the figure is also divided into two parts.
In such a structure, if the stylus 102 is vibrated by applying an alternating signal from electrodes of the vibrator 131, it vibrates in a resonance state along the axial direction. In this state, if the contact portion 121 comes in contact with a workpiece, a change occurs in the resonance state of the stylus 102. By measuring the change in the resonance state with an external detection circuit (not shown) via lead wire connected to electrodes of the detector 132, the contact between the contact portion 121 and the workpiece can be detected.
In the vibration-type contact detection sensor 100 as described above, the piezoelectric elements 103 are attached to the upper face and the lower face of the stylus support portion 112 with relatively high rigidity of the stylus holder 101 and thus vibration of the stylus 102 and state change thereof are propagated via the stylus holder 101, rather than directly to the detector 132. Therefore, vibration of the stylus 102 and state change thereof are attenuated in the stylus support portion 112 before they are propagated to the detector 132 and, thus, it is feared that the detection sensitivity of the detector 132 may be degraded.
Particularly, if the aspect ratio of the stylus 102 is large or the stylus 102 is formed of a soft material, attenuation of vibration of the stylus 102 in the stylus holder 101 becomes noticeable. Thus, the possibility that the change in the resonance state of the stylus 102 cannot be detected also occurs depending on the configuration or materials of the stylus 102.
Further, if the stylus 102 comes in contact with the workpiece from a direction orthogonal with the axial direction of the stylus, the stylus 102 is bent and the damage of the stylus 102 can be prevented. However, if the stylus 102 approaches and then comes in contact with the workpiece in the axial direction of the stylus, a relative movement of the stylus and the workpiece cannot be stopped instantaneously and, thus, the overrun occurs in the relative movement. In this case, excess stress is applied to the stylus 102 in the axial direction thereof due to the overrun and it is feared that the stylus 102 may sustain damage, such as plastic deformation or breakage; this is problem.
To circumvent such a problem, it is considered that limitations are imposed on the aspect ratio, the material, etc., of the stylus 102. However, for example, if the vibration-type contact detection sensor 100 is used with a small-hole measuring machine, a stylus with a large aspect ratio is required for measuring a small hole with a large aspect ratio, namely, the object to be measured varies depending on the measuring machine using the vibration-type contact detection sensor 100 and, thus, the configuration and the material of the demanded stylus also varies. For this reason, if limitations are imposed on the configuration, the material, etc., of the stylus 102, the number of types of measuring machines that can use the vibration-type contact detection sensor 100 and the number of types of objects to be measured are decreased; this is a problem.
Further, to circumvent the damage of the stylus by the contact of the stylus 102 with the workpiece in the axial direction of the stylus, a stylus axial direction escape mechanism is provided to prevent the stylus sustaining the damage. However, measurement accuracy is difficult to maintain due to the complicated structure and the cost of the whole sensor increases drastically.
It is an object of the invention to provide a vibration-type contact detection sensor that can detect contact with a workpiece with high sensitivity without limiting the configuration, material, etc., of a stylus.
To the end, according to a first aspect of the invention, there is provided a vibration-type contact detection sensor comprising a column-shaped stylus provided with a contact portion to be contacted with a workpiece at a tip end thereof; a vibrator for vibrating the stylus in an axial direction of the stylus; a detector for detecting contact of the contact portion with the workpiece based upon a change in vibration state of the stylus occurring when the contact portion and the workpiece come in contact with each other; a holder provided with a support portion for supporting the stylus, the vibrator, and the detector with the support portion, wherein at least the vibrator of the vibrator and the detector is fixed on the support portion of the holder and at least the detector of the vibrator and the detector is fixed to the stylus, and wherein the support portion of the holder and the stylus are disposed to be out of contact with each other.
In the above-mentioned sensor, it is preferable that the vibrator is adjusted so that the vibration of the stylus is at a resonance state.
According to the invention, the stylus is vibrated in a resonance state by the vibrator and the change in the resonance state of the stylus occurring when the contact portion and the workpiece come in contact with each other is detected by the detector, whereby the contact between the stylus and the workpiece can be detected.
The stylus is mounted directly on the detector and the detector is mounted directly on the holder, for example, whereby the vibration-type contact detection sensor is formed in a state in which the holder and the stylus are placed out of contact with each other and the stylus and the detector are placed in contact with each other.
Since the holder and the stylus are placed out of contact with each other, attenuation of vibration and state change (vibration change) of the stylus by the holder can be circumvented and the detector can detect vibration and state change of the stylus with high sensitivity. Therefore, the resonance state change of the stylus occurring when the contact portion of the stylus comes in contact with a workpiece can be detected with high sensitivity, so that contact with the workpiece can be detected with high sensitivity.
Vibration and state change of the stylus is not attenuated by the holder. Thus, if a stylus whose vibration attenuation is noticeable, a stylus with a high aspect ratio, a stylus formed of a soft material, or any other stylus is used with the vibration-type contact detection sensor, vibration and state change of the stylus can be detected reliably. Therefore, styluses of various configurations and materials are used matching the types of measuring machines and objects to be measured, so that the application range of the vibration-type contact detection sensor of the invention can be widened.
On the other hand, since the stylus and the detector are in contact with each other, vibration and state change of the stylus are propagated directly to the detector. Accordingly, if vibration change of the stylus occurring when the stylus comes in contact with a workpiece is slight, it can be detected by the detector reliably. Therefore, degradation of the detection sensitivity because of the configuration of the contact portion of the stylus can be prevented.
According to a second aspect of the invention, there is provided a vibration-type contact detection sensor comprising: a column-shaped stylus provided with a contact portion to be contact with a workpiece at a tip end thereof; a vibrator for vibrating the stylus in an axial direction of the stylus; a detector for detecting a contact of the contact portion with the workpiece from a change in vibration state of the stylus occurring when the contact portion and the workpiece come in contact with each other; a holder provided with a support portion, for supporting the stylus, the vibrator and the detector with the support portion, wherein at least the vibrator of the vibrator and the detector is fixed on the support portion of the holder and at least the detector of the vibrator and the detector is fixed to the stylus, and wherein the support portion of the holder and the stylus are disposed to be out of contact with each other. The support portion of the holder comprises a plurality of plate springs disposed substantially orthogonal with the stylus and parallel to each other and the plate spring is formed so that the stylus can be displaced in the axial direction thereof due to a slightly force.
According to the invention, the stylus is supported for displacement in the axial direction thereof. Therefore, if the contact portion of the stylus comes in contact with the workpiece in the axial direction of the stylus and the overrun occurs in the relative movement of the stylus and the workpiece, the stylus cannot be greatly deformed by the operation of the plate spring, and the whole stylus can be displaced in the axial direction of the stylus, whereby the damage of the stylus can be prevented.